The Auckland Primary Principals' Association (APPA) is telling members to boycott training to implement national standards.
Education Minister Anne Tolley said the group was grandstanding and members had already met with the ministry which was looking at its concerns.
APPA president Iain Taylor wrote to members that after "significant deliberation, APPA recommends that its members cease to attend any training around the implementation of the national standards".
The organisation said the policy was too flawed to work.
"The standards are not in fact standards and therefore cannot be moderated to provide valid, reliable and consistent achievement data," he said.
He said concerns raised by leading New Zealand academics in November last year had not been addressed. At the time the group said it was worried that the standards wrongly assumed children were failing if they did not meet the standard for their age; that labelling children as failures could harm learning and motivation; that the education system and students would suffer from public reporting of standards, ie league tables, and that the limited nature of the descriptions and standards without effective moderation would mean the information will be inconsistent and therefore unreliable.
"APPA believes the Government's national standards policy will not provide a solution to the Minister's issue of under-achievement," Mr Taylor said.
"APPA advises members to continue to use robust assessment practices in schools and report accurately to parents in plain language."
Mr Tayor said principals who attended national standards training found trainers had been unable to answer crucial questions around the standards.
He said the APPA would take further action if concerns were not addressed.
Green Party MP Catherine Dalahunty praised the APPA's action and said the policy should be reviewed in light of ongoing opposition, including an education union petition signed by 37,000 people presented to Parliament earlier in the week.
"National standards risk damaging the motivation and learning outcomes of many children. If they are used to produce public league tables as happens overseas, they could undermine the great work happening in many schools, particularly in low-decile areas," she said.
"(Education Minister) Anne Tolley has threatened to sack boards of trustees who refuse to implement the national standards, but she can't sack all the principals in Auckland.
"The message from the public and the Auckland principals is clear. Now it is the Government's move. Will John Key and Anne Tolley listen?"
Ms Tolley was unimpressed.
"This political grandstanding is a completely unprofessional approach from a group which has been ideologically opposed to the standards since the start," she said.
"This group met with the ministry recently and knows its concerns are already being addressed. Planning for the next round of professional development training is well under way and it incorporates the concerns and suggestions raised by principals."
Ms Tolley said the training was optional.
"Teachers and principals asked for it, which is why the Government is investing $26 million in this area. 84 per cent of schools took part in the first round of workshops.
"I'm disappointed the Auckland representatives made no attempt to share their concerns with me, but chose to follow the usual scaremonging approach through the media."
The sector, she said, was aware that changes would be made if needed.
"We are at the beginning of a three year process and if changes need to be made then that is what will happen - but we need to act now while one in five of our children are failing to learn the skills they need in reading, writing and maths.
"Rather than scoring political points I would encourage these principals to work with the standards to benefit our children."